Grounding and bonding are two very different issues for panels and sub-panels.
Sub-panels are in need of a free floating neutral back to the main disconnect and neutral and ground can’t be bonded together. That includes separate buildings.
(A neutral cannot be used as a ground and the neutral side of a sub-panel cannot be bonded to the sub-panel.)
Grounding and bonding are two very different issues for panels and sub-panels.
Sub-panels are in need of a free floating neutral back to the main disconnect and neutral and ground can’t be bonded together. That includes separate buildings.
(A neutral cannot be used as a ground and the neutral side of a sub-panel cannot be bonded to the sub-panel.)
1978 NEC 250-61(b) [page 164] … to current 2011 NEC 250.142(b)
The 1978 NEC side note states.“This section was rewritten in the 1978 NEC, to clarify intent”. This evidently was a requirement before 1978 and [NEC] thought it needed to be clarified that you can’t bond neutral and ground together. Hence, 4 wires/cables run for sub-panels for a very long time.
Almost any NEC Handbook will provide a graphic of sub-panel wiring showing the separation of ground and neutral with a free floating neutral back to the main disconnect panel. I’m certain the “How-To” books will also show the same as well as any Code Check book.
This is not true for installations in separate structures under the 2005 and earlier versions of the NEC. Here’s an article by Mike Holt under the 2005. It states this:
This may have been true for subpanels in the same building as the service, but as Robert points out above it is not always true. Detached building, without another metallic path back to the service building are a different animal are were allowed a 3 wire feeder and the neutral was re-bonded.
I was going to start a new thread but since this one is about seperate buildings and sub panels I’ll ask it here.
This is a sub panel in a detached garage. Four wire feed in an underground metal conduit. Grounds and neutrals are not seperate. Because of the metal conduit, these should be seperate and neutrals floating, correct? Also this panel needs its own exterior ground rod, correct? I did not find one.
Since this is a separate structure (detached garage) a GES (grounding electrode system) is required. That could be two ground rods or one of the other electrodes in Article 250.
As mentioned earlier in this thread separation between the EGC’s and the neutrals was not always required when certain conditions were met. That would depend on the code cycle under which this was installed. For a new installation you would need a 4 wire feeder (or 3 wire in a metallic raceway which can be the EGC), separate EGC and neutrals buses and a GES.
